The invention relates to a height-adjustable support for semitrailers or the like, comprising a locally fixed external support tube, an internal support tube, which is fixed to a nut on a spindle, the spindle being driven by a change-over gear and a bevel gear assembly. The change-over gear has two gear wheel stages which can be alternately activated, a separate gear stage comprising bevel gear toothing being provided for the distribution of forces after each gear wheel stage.
Supports of this type are disposed, generally in paired arrangement, as a supporting apparatus in the front region of the semitrailer.
An apparatus of this type is known from EP 0 675 0029. Here the speed-change gear mechanism is accommodated in a housing attached to the front of the support outer tube. The transmission input shaft and the transmission output shaft, on which the gearwheels are seated in a rotationally secure manner, are mounted respectively in the housing and in that wall of the support outer tube which lies opposite the housing. The transmission input shaft is in this case disposed below the bevel gear set, and alongside the spindle. The transmission output shaft is located above the ring gear, in whose upwardly directed toothing the bevel pinion seated in a rotationally secure manner on the transmission output shaft engages. The transmission input shaft can be rotated by means of a crank handle. The large gearwheel fitted on the transmission input shaft is provided in engagement with the smaller gearwheel, seated on the transmission output shaft, for a rapid height adjustment of the support; and the transmission generated by the pinion on the transmission input shaft with the large gearwheel on the gearwheel set of the transmission output shaft serves for the height adjustment of the support under load. Both in low-speed gear and in the faster height adjustment of this apparatus, the further power flow is effected via the bevel gear set to the spindle drive, and this apparatus is very bulky.
A pair of supports of the generic type is also known from EP 1 104 369 B1. The speed-change gear mechanism of this so-called apparatus for supporting the semitrailer of a truck tractor is disposed almost fully within the support, the transmission input shaft and the spindle disposed, for this purpose, outside the middle of the support being mounted in a common pillow block. The transmission input shaft and the transmission output shaft are mounted in a large cover, which is attached in protruding arrangement on the front wall of the support outer tube and which is also necessary to enlarge the installation space for the speed-change gear mechanism. The transmission input shaft arranged pointing to the spindle has a pinion, which engages in a large-diameter gearwheel of a gear set integral with the transmission output shaft and effects the transmission for a height adjustment under load. A further large-diameter gearwheel, which is mounted concentrically to the transmission input shaft, can be coupled and driven, following axial displacement of the transmission input shaft, by means of the pinion thereof. This latter large-diameter gearwheel hereupon engages in the pinion which belongs to the gear set of the transmission output shaft and via which the transmission for a faster adjustment of the support without load is realized. Disposed in a rotationally secure manner on the upper end of the spindle is a ring gear, in whose upward-pointing toothing the bevel pinion of the above-situated transmission output shaft engages. Here too, the bevel gear set is the second transmission stage both for the low-speed gear and for the faster adjusting process for the support.
In these known supports, it is particularly disadvantageous that behind the speed-change gear mechanism the power flow is effected always, i.e. both in the adjustment under load, the lifting process, and in the fast adjustment, the load-free height adjustment process, via one and the same bevel gear stage. Based on its large step-down ratio, the bevel gear stage is actually only fit for the lifting process. The result is that, in the previous transmission design for such supports, the speed increase attained via the step-up gear stage of the speed-change gear mechanism is very largely cancelled out by the step-down of the bevel gear set. And that the following spindle drive extends or retracts the support inner tube only at relatively moderate speed, even though this unsatisfactory process is referred to throughout the industry, for time-saving purposes, as the high-speed gear.
The object of the invention is to provide a height-adjustable support for semitrailers, which support has a particularly high high-speed gear in order to achieve a significant time gain, and in which all transmission parts are accommodated in the support outer tube without the need for a structural expenditure which enlarges the installation space.